PURPOSE: To reduce a welding equipment cost and to improve the welding efficiency by electrifying plural arc currents by changing the period by using a current control element and executing the electrification control of the arc current and filler wire current at different period.

CONSTITUTION: A TIG power source 3, wire heating power source 4 and the control circuit 2 of an output current are arranged on the plural electrodes HST power source 1 of two electrodes, etc. An HST welding is executed by alternately electrifying arc current and wire current and electrode A via the transistor Tr1 of the TIG power source 3 and that Tr3 of the wire heating power source 4. Moreover the welding of the reverse phase to an electrode A is executed by an electrode B via the transistor Tr2 of the TIG power source 3 and that Tr4 of the power source 4. The welding of plural places can thus be simultaneously executed with one unit of power source. Consequently the welding equipment cost is reduced and the welding efficiency is improved.